Various compounding ingredients conventionally are added to rubber or polymer compositions to enhance the physical and/or chemical properties of the compositions. Additives commonly added to rubber or polymer compositions include antioxidants, vulcanizing agents, accelerators, accelerator activators, plasticizers, softeners, tackifiers and extenders. In some cases it may be desirable to add other additives such as fillers, colorants, slip agents, lubricants, anti-bacterials, anti-statics, anti-corrosives (e.g., volatile corrosion inhibitors), anti-mildew agents, anti-settling agents, UV-protectants, insecticides, pesticides, oils (including biodegradable oils), etc., to a rubber or polymer composition.
In most instances to date, an additive or additives are combined with the rubber or polymer composition by mixing the rubber or polymer composition (or polymer composition pre-cursor) with the additive or additives together on a roll mill, in an internal mixer (such as a Banbury mixer) or within an extruder. During the mixing process, the rubber or polymer composition is masticated to convert the rubber or polymer composition into a more pliable form. With many polymers, the mastication of the polymer per se generates sufficient heat to cause the temperature of the mix to rise substantially. The increased temperature of the polymer causes the mix to become more pliable and permits the compounding ingredients to be more easily dispersed throughout the polymer. With some polymers, however, external heat is necessary to impart to the polymer the desired degree of plasticity. However, the temperature rise of the composition achieved during the mechanical mixing process or because of externally applied heat can be detrimental to some polymers. Such a temperature rise could cause degradation at temperatures realized during the mechanical mixing operation. Additionally, some additives cannot withstand the temperatures reached during the mechanical mixing procedure. For example, when incorporating various additives into polyvinyl chloride (PVC), the PVC often is heated to temperatures of up to about 180° C. to about 200° C. to cause the PVC to form a pliable plastic mass into which the additives can readily be incorporated. At such temperatures, the PVC commences to rapidly degrade. Even certain additives which might be considered desirable for use in PVC compositions cannot be used since at the processing temperatures achieved such additives would decompose or be otherwise objectionably affected. Many potential additives for rubber compositions also would be adversely affected by the temperatures reached during mixing of the composition on roll mills, in an internal mixer or in an extruder. Some ultra-fast accelerators, if added to a rubber batch being mixed on roll mills, in an internal mixer or in an extruder, would cause the rubber batch to “scorch” (pre-cure) during the mixing operation if the temperature of the rubber batch becomes too high.
U.S. Pat. No. 3,969,196 describes the separation of one organic compound from another using a supercritical fluid. In practicing the process, a supercritical fluid is placed in contact with a mixture of liquids and/or solids during which period one of the components in the mixture is dissolved in the supercritical fluid. The dissolved component is removed from the supercritical fluid by reducing the pressure of the supercritical fluid “solvent.”
U.S. Pat. No. 4,061,566 describes removing organic adsorbates which have been entrapped by a polymeric adsorbent using a supercritical fluid as an inert solvent for the adsorbate. The spent polymeric adsorbent, with the adsorbate adhered to it, is exposed to a supercritical fluid that is a solvent for the absorbate to cause the adsorbate to become dissolved in the supercritical fluid stream, thereby rejuvenating the adsorbent and rendering it capable of adsorbing more adsorbate. The adsorbate dissolved in the supercritical fluid is separated from the supercritical fluid solvent by reducing the temperature and/or pressure of the supercritical fluid to a subcritical state (to change the fluid from being a solvent for the adsorbate to being a non-solvent for the adsorbate) or by reacting the adsorbate with another material added to the supercritical fluid to form a compound readily separated from the fluid.
U.S. Pat. No. 4,250,331 pertains to an extraction process for recovering organic carboxylic acids from aqueous solutions of salts of the carboxylic acids. In utilizing the process, the aqueous solution is contacted with carbon dioxide in a supercritical state. The carbon dioxide reacts with the salt of the organic carboxylic acid in the solution to produce carboxylic acid which dissolves in the supercritical fluid. The supercritical fluid phase is separated from the aqueous phase. The pressure of the supercritical fluid is reduced which significantly reduces the solvent capabilities of the carbon dioxide, resulting in the carboxylic acid separating from the carbon dioxide. The carboxylic acid is removed from the carbon dioxide which can be re-pressurized and re-used.
A process for recovering tall oil and turpentine or their components is described in U.S. Pat. No. 4,308,200. The process involves contacting wood chips to be extracted with a fluid at supercritical conditions, the fluid being selected so that at supercritical conditions the fluid is a solvent for the components in the wood desired to be extracted. The supercritical fluid is maintained in contact with the wood chips until the desired degree of extraction is achieved. The tall oil and turpentine are retrieved from the supercritical fluid by reduction of the pressure of the fluid phase. By step-down reduction of the pressure, the various components of the tall oil and turpentine can be retrieved as separate fractions.
In addition to the extraction processes mentioned above, supercritical fluid extraction has been used for: removal of caffeine from coffee and tea; removal of nicotine from tobacco; deodorization of oils and fats; removal of vegetable oils and fats from seeds; de-asphalting petroleum fractions; removal of lanolin from wool; oil removal from potato chips; removal of monomer from polymer; removal of α-acids from hops; extraction of flavors and fragrances from lilac, lemon peel, black pepper, almonds, nutmeg, ground chilies, etc.; and extraction of oils, such as triglycerides, from soybean flake and corn germ. The aforesaid uses of supercritical fluids all concern extraction of a component from a complex matrix.
U.S. Pat. No. 4,112,151 describes a process for filling the pores of a resilient open-cell porous material with a pressure expressible material. The process can be used for filling the interconnecting cells of a resilient microporous rubber ink pad with ink. The process involves soaking the open-cell resilient material in a mixture of (a) a volatile solvent swelling agent for the resilient polymer and (b) the pressure expressible material. The volatile swelling agent swells the polymer material enlarging the interconnecting pores (cells) of the microporous material. The solvent/ink mixture then is able to enter and fill the enlarged pores (cells) of the microporous material. The volatile swelling agent then is allowed to evaporate from the microporous material leaving the pressure expressible material contained within the open cells of the microporous polymer.
U.S. Pat. No. 4,820,752 pertains to a process for infusing an organic additive into a polymer using a compressed fluid that is normally a gas at room temperature and pressure. The organic additive must have some degree of solubility in the compressed fluid and the solution of compressed fluid and organic additive must have some degree of solubility in the polymer. In accordance with the process, the solution of the normally gaseous fluid and organic additive and the polymer are brought into contact under pressure until a desired quantity of the solution is absorbed into the polymer. The compressed fluid then is diffused from the polymer leaving organic additive infused within the polymer.
Therefore, a process for incorporating additives into polymers that achieve uniform deep penetration of an additive into a polymer film or object without subjecting the polymer or additive to the relatively high temperatures encountered during mechanical mixing procedures would be extremely useful. Additionally, a process for incorporating one or more additives into a previously formed or “pre-formed” polymer film or object would be useful.